Structural and hydriding properties of amorphous MgNi with interstitially dissolved carbon

MgNiC_x with an amorphous structure were synthesized up to x=1.31 by mechanical alloying of amorphous (a-)MgNi and graphite as starting materials. The core-level X-ray photoelectron spectroscopy revealed that the original bonding states with metallic character of a-MgNi remained even in the sample with high carbon content although the graphite dissolved as interstitial carbon and it mainly bounded with Mg in a-MgNi. The crystallization temperature of MgNiC_x increased with increasing carbon content up to x=0.85, which was accompanied by a drastic change in the crystallization processes. Upon hydrogenation of MgNiC_x, the atomic ratio of hydrogen plus carbon to metal (H+C)/M remained a constant value of ≃0.9 through the whole system, indicating that carbon atoms dissolved into the sites that otherwise would have been occupied by hydrogen atoms.